This application is based upon and claims priority of Japanese Patent Applications No. 2002-16083, filed in Jan. 24, 2002, and No. 2001-213547, filed in Jul. 13, 2001, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a capacitor and a method of manufacturing the same and, more particularly, a capacitor having a ferroelectric layer or a high-dielectric layer and a method of manufacturing the same.
2. Description of the Prior Art
The high-dielectric layer such as the BST ((Ba,Sr)TiO3) layer, the ST (SrTiOx) layer, the Ta2O5 layer, etc. and the ferroelectric layer such as the PZT (PbZrxTi1-xO3) layer, etc. are widely used as the capacitor dielectric layer in DRAM (Dynamic Random Access Memory), FeRAM (Ferroelectric Random Access Memory), etc. by employing positively the high dielectric constant and the inverted polarization characteristic.
Also, in the ferroelectric capacitor of FeRAM, the planar-type capacitor having the structure in which the connection between the lower electrode of the capacitor and the impurity diffusion region of the transistor is extracted from the upper side of the lower electrode is practically used. In this case, the stacked-type capacitor having the structure in which the lower electrode is connected to the impurity diffusion region via the conductive plug formed immediately under the lower electrode is required in future to reduce the cell area.
If the high-dielectric oxide layer or the ferroelectric oxide layer is used as the capacitor dielectric layer, platinum (Pt) is widely used as the electrode material. This is because the conductivity of the platinum is high, the platinum can withstand the high-temperature process in the course of formation of the dielectric layer, the platinum can control the orientation direction of the capacitor dielectric layer formed thereon, etc.
On the contrary, the platinum has the high oxygen permeability. Therefore, if the lower electrode made of the platinum is formed on the plug in the stacked-type capacitor, the oxygen can transmit through the lower electrode in the annealing process in the course of the formation of the capacitor dielectric layer to oxidize the plug. As a result, for example, if the plug is formed of tungsten, the insulating tungsten oxide layer is formed between the plug and the lower electrode and thus the contact between the plug and the lower electrode is lost.
Therefore, in the stacked-type capacitor, the stacked structure such as the Pt/Ir structure in which the Ir layer and the Pt layer are formed sequentially from the bottom, the Pt/IrO2 structure in which the IrO2 layer and the Pt layer are formed sequentially from the bottom, the Pt/IrO2/Ir structure in which the Ir layer, the IrO2 layer, and the Pt layer are formed sequentially from the bottom, or the like is employed as the lower electrode structure.
The iridium (Ir) layer and the iridium oxide (IrO2) layer has the very small oxygen permeability and acts as the oxygen barrier in the annealing process. Therefore, if this layer is formed as the underlying layer of the platinum layer serving as the lower electrode of the stacked-type capacitor, the oxidation of the plug under the lower electrode can be prevented in the course of the formation of the capacitor dielectric layer.
For example, in Patent Application Publication (KOKAI) Hei 9-22829, it is proposed to use the Pt/IrO2/Ir structure as the lower electrode of the ferroelectric capacitor having the stacked structure. This structure succeeds in assuring the desired characteristic of the ferroelectric layer, while suppressing the oxidation of the lower layer structure of the capacitor by the annealing process in the oxygen atmosphere.
However, in the case that the PZT layer deposited by the sputtering method is applied as the capacitor dielectric layer, it is found that, if the lower electrode structure containing the iridium-based oxygen barrier layer (Ir layer, IrO2 layer) is employed, the increase in the leakage current of the capacitor is brought about.
If the PZT layer is deposited on the lower electrode by the sputtering, the as-deposited PZT layer is in the amorphous state and the high-temperature annealing process is needed to crystallize the PZT layer.
However, if the high-temperature annealing process is applied to crystallize the PZT layer after the amorphous PZT layer is deposited on the lower electrode having the structure in which the Pt layer is formed on the iridium-based oxygen barrier layer, the iridium element in the iridium-based oxygen barrier layer transmits through the Pt layer to diffuse into the PZT layer and then is introduced into the PZT crystal. As a result, the insulating property of the PZT crystal is lowered.
Such phenomenon can be avoided by growing the PZT layer that is in the crystal state on the lower electrode or crystallizing the PZT crystal at the low temperature. In this case, the dielectric constant of the formed PZT layer becomes small.
It is an object of the present invention to provide a capacitor capable of preventing the oxidation of the conductive plug formed immediately under the lower electrode and also preventing the metallic diffusion from the lower electrode to the capacitor dielectric layer in the course of the formation and the crystallization of the capacitor dielectric layer, and a method of manufacturing the same.
The above subject can be overcome by providing a capacitor which comprises a lower electrode having a structure in which a first conductive layer containing a first metal, a second conductive layer that is formed on the first conductive layer and made of a metal oxide of a second metal different from the first metal, and a third conductive layer that is formed on the second conductive layer and made of a third metal different from the first metal are formed sequentially; a dielectric layer formed on the lower electrode; and an upper electrode formed on the capacitor dielectric layer.
In the above capacitor, the first metal is iridium, the metal oxide of the second metal is a metal oxide of a platinum group metal except the iridium, and the third metal is the platinum group metal except the iridium.
In the above capacitor, the second metal is a same element as the third metal, and an interface conductive layer made of the second metal is further formed between the first conductive layer and the second conductive layer.
The above subject can be overcome by providing a capacitor manufacturing method which comprises the steps of forming a first conductive layer containing a first metal on an insulating layer; forming a second conductive layer made of a metal oxide of a second metal, that is different from the first metal, on the first conductive layer; forming a third conductive layer made of a third metal, that is different from the first metal, on the second conductive layer; forming a dielectric layer on a lower electrode; forming a fourth conductive layer on the dielectric layer; patterning the first conductive layer, the second conductive layer, and the third conductive layer to form a capacitor lower electrode; patterning the dielectric layer to form a capacitor dielectric layer; and patterning the fourth conductive layer to form a capacitor upper electrode.
In the capacitor manufacturing method, the second metal is a same element as the third metal, and the capacitor manufacturing method further comprises the step of forming an interface conductive layer made of the second metal between the first conductive layer and the second conductive layer.
According to the present invention, the capacitor is constructed by the lower electrode having the first conductive layer in which the first metal (e.g., iridium) is contained, the second conductive layer which is formed on the first conductive layer and made of the metal oxide of the second metal (e.g., the platinum group except the iridium), and the third conductive layer which is formed on the second conductive layer and made of the third metal (e.g., the metal of the platinum group except the iridium), the capacitor dielectric layer formed on the lower electrode, and the upper electrode formed on the capacitor dielectric layer.
According to the structure of such lower electrode, the diffusion of the oxygen into the conductive plug formed immediately under the lower electrode in the course of the layer formation of the capacitor dielectric layer can be prevented by the first conductive layer, and also the diffusion of the first metal from the first conductive layer to the capacitor dielectric layer can be prevented by the second conductive layer.
Therefore, the electric connection between the conductive plug and the lower electrode can be improved, and also the sufficient crystallization of the capacitor dielectric layer can be achieved while preventing the diffusion of the first metal into the dielectric layer after the dielectric layer is formed on the lower electrode. As a result, the high performance capacitor having the desired electric characteristics can be manufactured.
In addition, according to the present invention, the interface conductive layer made of the second metal, e.g., the metal of the platinum group except the iridium, is formed between the first conductive layer and the second conductive layer. Therefore, the (111) intensities of the third conductive layer and the ferroelectric layer can be enhanced and thus the electric characteristics of the ferroelectric capacitor can be improved.